Nickel is employed, as a pure metal or an alloy, in a variety of products. Nickel is largely used in stainless steel industry, along with chromium and molybdenum. Nickel use can be categorized into high-purity and lower-purity derivatives. High-purity derivatives, with at least 99% of nickel content (electrolytic nickel at 99.9% and carbonyl pellets at 99.7%) are usually used in metallurgical applications. Lower-purity derivatives, 20% to 96% of nickel content derivatives (ferro-nickel, matte, oxides and sinter) are generally employed in stainless steel industry and other steel alloys. Nickel scraps are also fed to siderurgy.
Nickel is generally obtained from laterite or sulfide ores. Laterite ores were a major source of early nickel. In 1950, less than 10% of worldwide production of nickel was provided from laterites, with sulfide deposits providing the bulk of nickel ore during that time period. Currently, production of nickel from sulfide ores has leveled off. As nickel demand continues to increase this gap may be fulfilled with laterite exploitation. Laterites correspond to about 70% of world land-based nickel resources, while accounting only for approximately 40% of nickel production. It is expected that approximately 51% of nickel production will be from laterite sources by 2012, based on the average rate of increase in production of 4% per year.
Laterite is a surface ore of red-brown color, generally found in hot and wet tropical areas. Laterite ore is rich in iron and aluminum and is produced by intensive and long lasting weathering, known as lateritization, of the underlying parent rock, such as ultramafic igneous rocks. Lateritization of ultramafic igneous rocks (serpentinite, dunite, or peridotite containing about 0.2-0.3% nickel) often results in a considerable nickel concentration. Laterites also consist mainly of the minerals kaolinite, goethite, hematite and gibbsite that form in the course of weathering. Moreover, many laterites contain quartz as relatively stable relic mineral from the parent rock.
Processing of laterite ores poses several problems. A major challenge faced by some processing plants is that solid-liquid separation stages are not very efficient. In particular, due to poor pulp settlement in a counter-current decantation (CCD) stage, roughly 10% of soluble nickel and cobalt are lost in rejects and in waste. Significant infrastructure investments have to be made to minimize such significant loss, such as utilizing a series of at least six large thickeners in solid-liquid separation to ensure proper solid settlement. Thus, a capital cost investment for a laterite ore processing plant utilizing conventional processes can be cost-prohibitive.
Numerous techniques have been explored for processing nickel laterite ore. U.S. Pat. No. 3,661,564 is directed to method for the recovery of nickel and cobalt from laterite with the elimination of iron, wherein the laterite is divided into a major and a minor portion and the minor portion is treated with hydrochloric acid to form a suspension. The major portion of laterite is mixed with the suspension to form a slurry which is roasted to form cobalt and nickel chloride. The nickel and cobalt chlorides are then dissolved by treating the solid residue with water, ferric chloride remaining in the residue. The solution is then subjected to a recovery treatment including cation exchange to separate the cobalt and nickel ions, and reduction to produce cobalt and nickel.
U.S. Pat. No. 3,892,639 discloses a method for the extraction of metal values from laterite ores including nickel, chromium, manganese, iron and cobalt by a series of steps including chlorinating the ore in a fluidized bed with hydrogen chloride gas to form volatile metal chlorides of nickel, iron, cobalt and manganese, and a residue containing chromium, removing and condensing the volatile chlorides to effect separation, recovering the metals of nickel, cobalt and manganese and chlorine as by the use of electrolytic cells, reacting the iron chloride with oxygen to separate the iron as iron oxide; removing the residue from the fluid bed reactor for reduction with carbon to produce carbides; leaching to form salts of chromium, separating from other salts, and recovering the chromium.
U.S. Pat. No. 5,571,308 relates to a method for recovering nickel from high magnesium-containing lateritic ores which also contain iron. The ores which are referred to as saprolitic ores are subjected to leaching with a mineral acid from the group consisting of HCl, H2SO4 and HNO3. Following leaching with HCl, for example, the pregnant solution obtained is separated from undissolved solids and the nickel is preferably recovered by contacting the solution with a resin selective to nickel absorption. The raffinate remaining which contains iron and magnesium chlorides may be subjected to pyrohydrolysis to produce their respective oxides and free HCl for recycle into the leaching system. The nickel is extracted from the resin using a stripping solution of said acid, and the nickel thereafter extracted from the nickel-loaded stripping solution.
Several chloridization processes are described in the following International Publications Nos. WO/2002/008477, WO/2002/053788 and WO/2007/106969. International Publication No. WO/2002/008477 discloses a method for the recovery of nickel, cobalt, iron, chromium and magnesium species from laterite ores by a series of steps which include grinding the ore to produce particles; chlorinating the ore by first subjecting them to gaseous hydrochloric acid and secondly, by curing them with concentrated HCl to form water soluble salts of nickel, cobalt, iron, chromium and magnesium, filtering the solution; selectively recovering nickel and cobalt by a process selected from the group of processes consisting of electrowinning, solvent extraction, specific ion-exchange resins and sulfide precipitation.
International Publication No. WO/2002/053788 is directed to a method for the recovery of base metals such as cobalt, nickel, copper, lead, zinc, mercury and cadmium, precious metals such as silver and gold, as well as the platinum group metals, comprising ruthenium, rhodium, palladium, osmium, iridium and platinum from fresh ore, mine tailings and industrial wastes by a series of steps which include analyzing the ore, mine tailings or industrial wastes to determine the presence of one or more of the above mentioned metals; chloridating the ore with a strength determined by the presence of the most refractory of the metals ascertained by the analyzing step, in the presence of a source of chloride ions in an amount determined by the metals present to form a solution of metal chlorides and a sterile residue; separating the solution of metal chlorides from the residue to produce a filtered solution of metal chlorides; recovering the metal chlorides from the filtered solution of metal chlorides to produce a barren solution; recycling the source of chloride ions.
International Publication No. WO/2007/106969 relates to an essentially open-circuit process for recovering value metal species from a laterite-type feedstock, the process comprising the sequential or unsequential steps of separating the laterite-type feedstock into a first and a second fraction; reacting an acid with a chloride salt in a first compartment, thereby generating gaseous HCl; chlorinating the first fraction with the gaseous HCl in a second compartment, thereby producing a chlorinated fraction, wherein excess HCl is recovered and dissolved in water, thereby producing a concentrated HCl solution; combining the chlorinated fraction and the second fraction into a mixture; leaching the mixture with the concentrated HCl solution in a third compartment, thereby producing a reaction mass; submitting the reaction mass to a separation of phases, thereby separating an insoluble residue from a head solution; and selectively recovering value metal species from the head solution.
U.S. Pat. No. 7,329,396 discloses a process for leaching a value metal from oxidic materials, such as a lateritic nickel ore, comprising the step of leaching the ore with a lixiviant comprising a cationic salt (e.g., magnesium chloride) and hydrochloric acid is disclosed. An oxidant or additional metal chloride (such as that which results from the leaching operation) may be added. In one embodiment, the process comprises recovery of a value metal from ore comprising the steps of leaching the ore with a lixiviant; separating a value metal-rich leachate from the ore in a first solid-liquid separation; oxidizing and neutralizing the value metal-rich leachate so obtained; and separating a solution of magnesium chloride from the leachate so obtained in a second solid-liquid separation. In another embodiment, the lixiviant solution is regenerated from the solution of magnesium chloride.
Although a significant effort has been put into chloridization of base metal oxides, all processes developed so far have failed to do so effectively. Most chloridization processes discussed above require high temperatures and specialized engineering solutions to deal with corrosiveness of HCl. Some of the processes discussed above which do exploit low temperature chloridization are problematic in terms of downstream processing, as they need costly and complex iron and aluminum removal stages. Thus, there is a need for an improved chloridization process that simplifies downstream processing.